The ornamental design for a double clasp for jewelryitem, as shown and described.
FIG. 1 is perspective view of a new design for a double clasp for jewelry item; and,
FIG. 2 is another perspective view of the new design for a double clasp for jewelry item.
The broken lines in the figures form no part of the claimed design. The portions of the double clasp for jewelry item that are not visible in the figures form no part of the claimed design.